Flexible transparent thin film transistor (TFT) based on indium gallium zinc oxide (IGZO) was first reported by Hosono at Tokyo Institute of Technology, Japan in 2004. Since then IGZO-TFT had attracted much attention from both academic institutes and industry. Its application in the field of display technologies, especially in new display equipments, has been explored.
As a new type of passively driven circuit, IGZO-TFT is used in flat panel display devices, but there are still many problems to be resolved before it enters the commercialization stage.
IGZO layer is very sensitive to the process conditions, particularly to the hydrogen atoms in the air. The hydrogen atoms may cause the electrical properties of the device to change and even change the passive layer from semiconductor to conductor. A protective layer is usually plated on top of the IGZO layer. SiNx prepared by plasma enhanced chemical vapor deposition (PECVD) is generally used as the protective layer for the commercial amorphous silicon TFT. However, SiNx is not able to be used as the protective layer for IGZO-TFT, because the SiNx prepared by PECVD contains a large number of hydrogen atoms. The protective layer currently used for IGZO layer is SiOx, which is prepared by plasma enhanced chemical vapor deposition (PECVD).
In the fabrication of the IGZO layer, however, there still involved such non-vacuum processes as photoresist coating, exposure, and development, and a certain amount of hydrogen atoms may exist in these processes. Also, in the subsequent PECVD coating of SiOx, there may be present some hydrogen atoms either. These hydrogen atoms are likely to affect the performance of IGZO layer, and no solution to solve this problem has been found yet.